Floral nectaries from Limodorum abortivum (L) Sw and Epipactis atropurpurea Rafin (Orchidaceae): ultrastructural changes in plastids during the secretory process

Abstract

Summary — Ultrastructural features of the floral nectaries of 2 orchid species, Limodorum abortivum (L) Sw and Epipactis atropurpurea Rafin, were compared. In particular, ultrastructural changes were followed in the plastids throughout the process of nectar secretion. There is evidence that plastids play an important role in this process. Before secretion begins, plastids of epidermal and subepidermal cells of the nectaries of both species, accumulated large quantities of starch. However, during the phase of nectar secretion, the plastids were found to contain little if any, starch, suggesting that starch degradation had augmented nectar sugar production. Plastoglobuli were evident during all developmental stages. The tubular reticulum found in plastids of pre-secretory nectaries was still evident during secretion, but was then found to contain an unknown, dense osmiophilic material. The floral nectary of L abortivum is sucrose dominant, whereas that of Eatropurpurea is hexose rich. Therefore, the differences in nectar-carbohydrate composition are apparently not explainable by the similar ultrastructural changes of their floral nectaries. Further investigation is required to determine the biochemical basis for the disparity in nectar sugar composition between these 2 species.

Secretion and composition of nectar and the structure of perigonal nectaries in Fritillaria meleagris L. (Liliaceae)

“…Similar cuticular pores have been recorded for the nectary hairs of Abutilon (Findlay and Mercer 1971). In some plants, however, the secretion is released via a disrupted cuticle, as in the nectaries of Limodorum abortivum (Pais and Figueiredo 1994). In others, such as Platanthera chlorantha (Stpiczyńska 2003a, b), the cuticle is completely permeable to secreted substances, as well as resorbed nectar.…”

Studies on the ultrastructure of a three-spurred fumeauxiana form of Anacamptis pyramidalis

“…In the osmophore cells of Stanhopea (Curry et al 1988) the smooth endoplasmic reticulum (SER) was, furthermore, responsible for transport and/or synthesis of terpenoids. The proximity of SER and plastids were also pointed out in studies of the ultrastructure of the nectary spur of Limodorum abortivum (Pais and Figueiredo 1994) and P. bifolia (Stpiczyńska 1997). A dense osmiophilic material and tubular structures had been reported in plastids occurring in the nectaries of other orchid species (Pais and Figueiredo 1994;Stpiczyńska and Matusiewicz 2001;Stpiczyńska et al 2004Stpiczyńska et al , 2005 and from glandular trichomes involved in terpenoid synthesis (Cheniclet and Carde 1985;Turner et al 2000), in which the plastids were also in close association with ER.…”

“…Starch-less plastids are believed to secrete lipid-soluble odours, for example monoterpenes (Fahn 1988). The hypothesis of plastid involvement in fragrance synthesis, because of the close vicinity of plastoglobuli and intraplastidal membranes and the plastid envelope and SER, has been broadly discussed by many researchers (Bosabalidis and Tsekos 1982;Curry 1987;Pais and Figueiredo 1994;Stpiczyńska 1997). In form fumeauxiana the numerous profiles of ER were in close vicinity and in contact with plastids.…”

Anatomy and ultrastructure of floral nectary of lnula helenium L (Asteraceae)

“…Descriptions in literature show that nectar can be secreted outside through the walls of the secretory cells (Rachmilevitz and Fahn 1973;Pais and Figueiredo 1994), of trichomes (Sawidis et al 1989;Sawidis 1998), or it can be released through the modified stomata (Nepi et al 1996;Weryszko-Chmielewska et al 2003;Weryszko-Chmielewska et al 2004;Davis et al 2005). In the nectaries of elecampane, nectar was secreted through the stomata.…”